Hydrocarbon stripping process



3U, i967 s. D. LAWSON 3,322,667

HYDROGARBON STRIPPING PROCESS Filed May 11, 1964 RAF'FINATE 10 JSTRIPPERVAPOR ONE TDEWAXING PROCESS 22 RAFF lNATE Q LIQUID PROPANE INVENTOR. S.D. LAWSON A TTORNEKS 3,322,667 HYDROCARBON STRIPPING PROCESS Shelby ll).Lawson, Bartlesville, Okla, assignor to Phillips Petroleum Company, acorporation of Delaware lFiled May 11, 1964, Ser. No. 366,581 8 "Claims.(Cl. 208356) This invention relates to a process for steam stripping ahydrocarbon. In another aspect, this invention relate to a process forseparating a solvent from a hydrocarbon. In yet another aspect, thisinvention relates to an improved process for the production ofhydrocarbon lubricating oils utilizing a solvent extraction process stepfollowed by a solvent dewaxing process step.

It is known in the art to produce lubricating oils by various processescomprising distillation, solvent extraction, dewaxing process steps, andthe like. In general, three types of hydrocarbons are to be found in thelubricating oil fraction of a crude petroleum, namely, paraffinic,aromatic, and naphthenic hydrocarbons. It is known that the paraflinictype of hydrocarbons have the highest viscosity indices whereasnaphthenic and aromatic type hydrocarbons have materially lowerviscosity indices. As a result of this, it is desirable that the productlubricating oil contain high concentrations of paraffinic typehydrocarbons and minimum concentrations of naphthenic and aromatic typehydrocarbons.

In order to produce lubricating oils having high concentrations ofparaffinic type hydrocarbons, lubricating oil fractions of a crudepetroleum are subjected to a solvent extraction process wherein thelubricating oil fraction is contacted with a solvent selective to theremoval of the aromatic type hydrocarbon compounds. The solventsconventionally employed for the removal of the aromatic type compoundsare less selective for removing naphthenic constituents.

When, for example, phenol or phenol containing a low concentration ofwater is employed as the selective solvent, the rafiinate phasecomprising the paraflinic hydrocarbon fraction is passed to a strippingzone wherein small concentrations of phenol withdrawn from theextraction zone with the raifinate is steam stripped from the raflinate.The steam stripped raflinate is passed to a dewaxing zone wherein highpour point waxy materials are separated from the rafiinate.

A conventional process for dewaxing the raflinate obtained from thesolvent extraction step comprises reducing the temperature of theraflinate at a controlled rate to precipitate the wax crystals by theevaporation of a light hydrocarbon such as propane. During the chillingprocess, the wax crystals form and remain suspended in the propane-oilsolution. The chilled slurry is then charged to a filter for separationof the formed wax crystals from the oil.

The steam stripped raffinate passed to the dewaxing process stepconventionally contains water which interferes with the dewaxing step,forming ice crystals during the chilling step. To prevent the formationof ice crystals in the dewaxing process, resulting in a substantialreduction in filter efliciency and operation of other dewaxingequipment, it is necessary that water contained in the raffinate feed tothe dewaxed process be removed.

Accordingly, an object of my invention is to provide an improved processfor steam stripping a hydrocarbon.

Another object of my invention is to provide an improved process forstripping solvent from a hydrocarbon.

Another object of my invention is to provide a process for theseparation of water in the hydrocarbon feed to a dewaxing process.

Other objects, advantages and features of my invention will be readilyapparent to those skilled in the art from 3,322,667 Patented May 30,1967 the following description, the drawing and appended claims.

By my invention, I have provided a process wherein a hydrocarbon issteam stripped and the steam stripped hydrocarbon contacted with avaporous drying agent. Preferably, although not to be limited thereto,the steam stripping and drying steps are conducted in the same vessel.

The invention is applicable to the separation of liquids fromhydrocarbons wherein said liquids are more readily volatilized in thepresence of steam than said hydrocarbons. Although not to be limitedthereto, the invention is particularly applicable to the separation ofsolvents such as phenol and furfural from hydrocarbon lubricating oilfractions.

The vaporous drying agents employed in the process of my invention arethose more volatile than the hydrocarbon feed to the drying zone andpreferably more readily volatilized than water. In a process wherein ahydrocarbon is solvent extracted and subjected to a subsequent processstep, such as a dewaxing process wherein the said hydrocarbon iscontacted with an agent more readily volatilized than said hydrocarbon,it is preferred that the vaporous drying agent employed in the dryingstep be the same agent employed in the subsequent process step. Agentsemployed in hydrocarbon dewaxing processes and found to be suitable asvaporous drying agents include butane, propane, methyl ethyl ketone, amixture of ketones, and a mixture of methyl ethyl ketone and toluene.

Although not to be limited thereto, the invention will hereinafter bedescribed as applied to a raffinate obtained from a phenol solventextraction process, said raffinate to be subjected to a subsequentdewaxing process. It will be understood by those skilled in the art thatthe invention is applicable to hydrocarbons withdrawn from other solventextraction zones such as a furfural extraction zone. The term raffinateas herein employed refers to a lubricating oil fraction that has had thearomatics removed therefrom and contains high pour point waxy materials.It will also be understood by those skilled in the art that theinventive stripping process can be applied to the extract obtained fromthe phenol solvent extraction process as well as to hydrocarbons ingeneral.

The drawing is a schematic representation of one em-' bodiment of theinvention.

Although not to be limited thereto, in the stripping of phenol from ahydrocarbon ratlinate, the weight ratio of stripping steam tohydrocarbon feed is maintained generally in the range of 1:150 to 1:500.Temperatures and pressures in the solvent stripping region of thestripping zone are normally maintained in the range of 350 F. to 700 F.,and 10 p.s.i.a. to 20 p.s.i.a., respectively. The weight ratio ofpropane, when employed, to hydrocarbon in the drying region of thestripping zone is generally maintained in the range of 1:500 to 112000.Temperatures and pressures in the drying region are generally maintainedin the range of 350 F. to 700 F., and 10 p.s.i.a. to 20 p.s.i.a.,respectively. The stripping tower may or may not be reboiled. Usuallythe oil is charged at sufiicient temperature that no additional heatingis required.

Referring to the drawing, a rafiinate having a viscosity of SSU at 210F. and containing phenol and obtained from the phenol solvent extractionof a lubricating oil hydrocarbon fraction is passed via conduit means 11to the top tray of a 24- tray stripper 10 at the rate of barrels perhour.

A mixture of Ellenberger and Burbank crude oils was subjected toatmospheric distillation to produce a topped crude. This topped crudewas subjected to vacuum distillation to produce distillates of a gasoil, a 10 raw, and a 20 raw lubricating oil base stock. The vacuumreduced crude was subjected to propane deasphalting, producing a 50 rawand a 250 raw lubricating oil base stock. These raw stocks wereseparately subjected to phenol extraction. The raftinate of the examplewas produced in the above manner.

165 pounds stripping steam at the rate of 150 pounds per hour is passedvia conduit means 12 to the fourth tray of stripper 10. Vaporous propaneat the rate of 40 pounds per hour is passed via conduit means 13 to thelower region of stripper 10. Stripper 1 is operated at a bottomtemperature of 500 F., a top temperature of 500 F., and a top pressureof 18 inches of water vacuum. The vacuum is maintained within stripperby a conventional steam ejector 20.

Within stripper 10 the hydrocarbon feed is initially contacted withsteam. The stripped hydrocarbon free of solvent and containing moisturepasses downwardly from the steam' contact region through stripper 10into the drying region and is contacted therein with the rising vaporouspropane. The propane separates the water from the stripped hydrocarbon.

A vapor stream comprising steam, propane and phenol is drawn fromstripper 10 via conduit means 14 and passed to a conventional heatexchange means 16. A partially condensed stream is passed from heatexchange means 16 via conduit means 17 to accumulator 18. A liquidstream comprising phenol and water is withdrawn from accumulator 18 viaconduit means 21. The water and phenol stream withdrawn from accumulator18 via conduit means 21 can be passed, if desired, to a subsequentseparation step not herein illustrated for recovery of the phenol fromthe water. A vapor stream comprising steam and propane is withdrawn fromthe top of accumulator 18 via conduit means 19.

Rafiinate substantially free of phenol and water is withdrawn from thebottom of stripper 10 via conduit means 22 at the rate of 48,000 poundsper hour. Although as illustrated, the steam stripping and drying stepswere conducted in the same stripper vessel, it is within the scope ofthis invention to employ separate vessels for the steam stripping andvaporous drying steps. The rafiinate withdrawn from stripper 10 viaconduit means 22 can be passed to a subsequent propane dewaxing process23; wherein liquid propane is introduced into said dewaxing process vialiquid propane conduit means 24. Under such conditions, the propaneabsorbed by the rafiinate in the drying region is separated from theraftinate in the pro pane dewaxing process.

It is also within the scope of this invention to separate absorbeddrying agent from the rafiinate withdrawn from stripper 10 via conduitmeans 22 by a subsequent conventional separation process step not hereinillustrated.

As will be evident to those skilled in the art, various modifications ofthis invention can be made, or followed, in the light of the foregoingdisclosure, without departing from the spirit or scope thereof.

I claim:

1. A process which comprises contacting a mixture com-prising ahydrocarbon and a component selected from phenol and furfural with steamin a stripping zone, and contacting the resultant steam-strippedhydrocarbon with a vaporous drying agent selected from butane, propane,methylethyl ketone, mixtures of ketones, and a mixture of methylethylketone and toluene.

2. A process which comprises introducing a feed mixture comprising ahydrocarbon and a component selected from phenol and furfural into theupper region of a stripping zone, introducing steam into an intermediateregion of said stripping zone, introducing a vaporous drying agentselected from butane, propane, methylethyl ketone, mixtures of ketones,and a mixture of methylethyl ketone and toluene into the lower region ofsaid stripping zone, Withdrawing a vaporous fraction comprising steam,said component, and said drying agent from the top of said strippingzone, and withdrawing a substantially water-free hydrocarbon fractionfrom the bottom of said stripping zone.

3. A process which comprises contacting a rafiinate containing aselective solvent having a greater volatility than said ralfinate withsteam in a stripping zone, contacting with a vaporous dewaxing agent theresultant solvent-free raffinate in said stripping zone whereby saidrafiinate is rendered substantially water-free, passing the resultantsubstantially water-free and solvent-free raliinate from said strippingzone to a dewaxing zone, adding to said dewaxing zone as a liquid anadditional amount of dewaxing agent precipitating wax crystals in saiddewaxing zone by the vaporization of said dewaxing agent, andwithdrawing from said dewaxing zone a substantially wax-free lubricatingoil fraction.

4. The process of claim 3 wherein each said dewaxing agent is selectedfrom the group consisting of butane, propane, methyl ethyl ketone, amixture of ketones, and a mixture of methyl ethyl ketone and toluene.

5. The process of claim 4 wherein said selective solvent is selectedfrom the group consisting of phenol and furfural.

6. A process which comprises contacting a rafiinate containing phenolwith steam in the solvent-stripping region of a stripping zone,contacting with vaporous propane the resultant phenol-free raffinate inthe drying region of said stripping zone, maintaining a temperature andpressure in said drying region in the range of 350- 700 F. and 10p.s.i.a. to 20 p.s.i.a., respectively, maintaining the weight ratio ofvaporous propane to rafiinate in said drying region in the range of1:500 to 112000, passing the resultant moisture-free and phenol-freerallinate from said stripping zone to a dewaxing zone, precipitating waxcrystals in said dewaxing zone by the vaporization of propane introducedinto said dewaxing zone as a liquid, and withdrawing from said dewaxingZone a substantially wax-free lubricating oil fraction.

7. The process of claim 6 to include maintaining a temperature andpressure in said solvent stripping region of said stripping zone in therange of 350-700" F. and 10 p.s.ia. to 20 p.s.i.a., respectively, andmaintaining the weight ratio of said steam to said raffinate in therange of 1:150 to 1:500.

8. A process which comprises introducing a feed mixture comprising ahydrocarbon and phenol into the upper region of a stripping zone,introducing steam into an intermediate region of said stripping zone,introducing propane into the lower region of said stripping zone,withdrawing a vaporous traction comprising steam, said phenol, and saidpropane from the top of said stripping zone, and withdrawing asubstantially water-free hydrocarbon fraction from the bottom of saidstripping zone.

References Cited UNITED STATES PATENTS 2,192,253 3/1940 Adams 20832l2,673,174 3/1954 King 208- 321 2,687,982 8/1954 Baumann 208321 2,692,22210/1954 Packie 208321 DELBERT E. GANTZ, Primary Examiner.

HERBERT LEVINE, Examiner.

S. P. JONES, Assistant Examiner.

1. A PROCESS WHICH COMPRISES CONTACTING A MIXTURE COMPRISING AHYDROCARBON AND A COMPONENT SELECTED FROM PHENOL AND FURFURAL WITH STEAMIN A STRIPPING ZONE, AND CONTACTING THE RESULATANT STEAM-STRIPPEDHYDROCARBON WITH A VAPOROUS DRYING AGENT SELECTED FROM BUTANE, PROPANE,